Fig. 7

Basic properties of lesion-associated extracellular spikes. a 25 s example of spontaneous, transient spike generation in superficial layers (cortical layer 2, L2) on the side of the brain ipsilateral to the tumour cell implantation site. Note concurrent recordings from deep (cortical layer 5, L5) layers demonstrated no spiking. b Example L2 recordings demonstrating the variability of spike generation. Illustrated is an example of the most common discharge – pairs of field spikes or relatively broad halfwidth and an example of a narrow halfwidth initial spike leading to a polyspike-like pattern of afterdischarge. Graph shows distribution of initial spike halfwidths (normalised to maximum incidence) for 138 spontaneous events from n = 4 slices from N = 2 mice. Note the multimodal nature of the distribution of spike widths. c Spikes were highly localised annularly around the radial walls of the lesions in L2. Cartoon illustrates four recording sites at different positions from the core of the lesion in L2. Example traces taken from each of these positions reveal multi-unit activity only within the body of the lesion, multi-unit and field spike at the border of the lesion and field spike only extending < 200 μm tangentially from this. Scale bars 0.1 mV, 2 s (a), 0.5 s (b), 0.1 s (c)